U.S. patent number 8,289,201 [Application Number 11/758,785] was granted by the patent office on 2012-10-16 for method and apparatus for using non-linear ground penetrating radar to detect objects located in the ground.
This patent grant is currently assigned to The Boeing Company. Invention is credited to Sandor Holly, Nicholas Koumvakalis, Robert Alan Smith.
United States Patent |
8,289,201 |
Holly , et al. |
October 16, 2012 |
Method and apparatus for using non-linear ground penetrating radar
to detect objects located in the ground
Abstract
A method and apparatus for detecting objects located
underground. In one advantageous embodiment, a detection system
detects objects having electrical non-linear characteristics
located underground. The detection system comprises a transmitter
unit, a receiver, and a processor. The transmitter transmits a
plurality of pulsed radio frequency signals having a first
frequency and a second frequency into a ground. The receiver
monitors for a response radio frequency signal having a frequency
equal to a difference between the first frequency and a second
frequency, wherein the response radio frequency signal is generated
by an object having the non-linear conductive characteristics in
response to receiving the plurality of electromagnetic signals. The
processor is connected to the transmitter unit and the receiver,
wherein the processor controls an operation of the transmitter unit
and the receiver, wherein the object is detected when the response
radio frequency signal is detected by the receiver.
Inventors: |
Holly; Sandor (Woodland Hills,
CA), Koumvakalis; Nicholas (Thousand Oaks, CA), Smith;
Robert Alan (Hampton Cove, AL) |
Assignee: |
The Boeing Company (Chicago,
IL)
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Family
ID: |
46795041 |
Appl.
No.: |
11/758,785 |
Filed: |
June 6, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120229321 A1 |
Sep 13, 2012 |
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Current U.S.
Class: |
342/22; 342/134;
342/90; 342/89; 342/196; 342/175; 342/27; 342/192; 342/135;
342/118; 342/82; 342/195 |
Current CPC
Class: |
G01S
7/41 (20130101); G01V 3/17 (20130101); G01S
13/885 (20130101); F41H 11/136 (20130101) |
Current International
Class: |
G01S
13/04 (20060101); G01V 3/12 (20060101); G01V
3/00 (20060101); G01S 13/00 (20060101) |
Field of
Search: |
;342/21,22,27,28,59,82,89,118,134-145,175.188-197,90 ;175/24,26
;324/600,629,637,642-646 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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WO 00/77614 |
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Dec 2000 |
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WO |
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WO 2006/110991 |
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Oct 2006 |
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WO |
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Other References
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12/026,918, pp. 22. cited by other .
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12/504,293, pp. 21. cited by other.
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Primary Examiner: Gregory; Bernarr
Attorney, Agent or Firm: Yee & Associates, P.C.
Claims
What is claimed is:
1. A detection system for detecting objects having electrical
non-linear characteristics located underground, the detection
system comprising: a transmitter unit for transmitting into a
ground a first pulsed radio frequency signal at a first frequency
generated by a first transmitter and a second pulsed radio
frequency signal at a second frequency generated by a second
transmitter; and a receiver for monitoring for a response radio
frequency signal having a third frequency equal to a difference
between the first frequency and the second frequency, wherein the
response radio frequency signal is generated by an object having
non-linear conductive characteristics in response to receiving the
first pulsed radio frequency signal at the first frequency and the
second pulsed radio frequency signal at the second frequency; and a
processor for controlling an operation of the transmitter unit and
the receiver, wherein the processor is connected to the transmitter
unit and the receiver, and wherein the object is detected when the
response radio frequency signal is detected by the receiver.
2. The detection system of claim 1, wherein the processor controls
the transmitter unit to change the first frequency and the second
frequency such that the frequency of the response radio frequency
signal changes through a range of frequencies.
3. The detection system of claim 1, wherein the processor executes
a program to interpret the response radio frequency signal.
4. An apparatus comprising: a transmitter unit for transmitting,
into a ground, a first electromagnetic signal having a first
frequency and a second electromagnetic signal having a second
frequency; and a receiver for monitoring for a third
electromagnetic signal having a third frequency equal to a
difference between the first frequency and the second frequency in
which the frequency is generated by an object having an electrical
non-linear conductive characteristic in response to being exposed
to the first electromagnetic signal having the first frequency and
the second electromagnetic signal having the second frequency,
wherein the object is detected when the third electromagnetic
signal having the third frequency is detected by the receiver.
5. The apparatus of claim 4, wherein the plurality of
electromagnetic signals are pulsed radio frequency signals.
6. The apparatus of claim 4, wherein the plurality of
electromagnetic signals are continuous wave radio frequency
signals.
7. The apparatus of claim 4 further comprising: a processor
controlling a selection of the first frequency and the second
frequency, wherein the processor is connected to the transmitter
unit and the receiver.
8. The apparatus of claim 4, wherein the processor executes
instructions to analyze electromagnetic signals received by the
receiver to provide an interpretation of the electromagnetic
signals.
9. The apparatus of claim 4 wherein the transmitter unit comprises
a first transmitter and a second transmitter and wherein the first
transmitter generates electromagnetic signals in the plurality of
electromagnetic signals having the first frequency and the second
transmitter generates electromagnetic signals in the plurality of
electromagnetic signals having the second frequency.
10. The apparatus of claim 4, wherein the difference frequency is
predetermined.
11. The apparatus of claim 4, wherein the first frequency and the
second frequency change to change the difference frequency, wherein
the difference frequency changes through a range of
frequencies.
12. The apparatus of claim 4, wherein the first frequency and the
second frequency are selected to penetrate the ground to a selected
depth in the ground.
13. The apparatus of claim 4, wherein the electrical non-linear
characteristic is a metal with corrosion in portions of the
metal.
14. A method for detecting an object with electrical non-linear
characteristics, the method comprising: transmitting into a ground,
a first electromagnetic signal having a first frequency and a
second electromagnetic signal having a second frequency; monitoring
for a third electromagnetic signal having a third frequency equal
to a difference between the first frequency and the second
frequency, wherein the third electromagnetic signal is generated by
an object in ground having an electrical non-linear characteristic
in response to being exposed to the plurality of electromagnetic
signals; and detecting the object having the electrical non-linear
characteristic when the third electromagnetic signal is
detected.
15. The method of claim 14, wherein the transmitting step
comprises: transmitting a plurality of pulsed radio frequency
signals having the first frequency and the second frequency.
16. The method of claim 14, wherein the transmitting step
comprises: transmitting a plurality of continuous wave radio
frequency signals having the first frequency and the second
frequency.
17. The method of claim 14 further comprising: interpreting the
electromagnetic signal received by the receiver.
18. The method of claim 14, wherein the transmitting step
comprises: transmitting a plurality of electromagnetic signals
having the first frequency and the second frequency into the ground
in which the first frequency and the second frequency change to
change the frequency through a range of frequencies.
19. The method of claim 14, wherein the electrical non-linear
characteristic is a metal with corrosion in portions of the
metal.
20. The method of claim 14, wherein the object is one of a tunnel,
a bunker, an electronic instrument control system, a computer, or
communication equipment.
Description
CROSS REFERENCE TO RELATED APPLICATION
The present invention is related to the following patent
application: entitled "Method and Apparatus for Locating Objects
Using Radio Frequency Identification", Ser. No. 11/758,787, filed
even date hereof, assigned to the same assignee, and incorporated
herein by reference.
BACKGROUND INFORMATION
1. Field
The present invention relates generally to improved method and
apparatus for identifying objects. Still more particularly, the
present invention relates to a method and apparatus for detecting
objects located in the ground using electromagnetic radiation.
2. Background
An increasing demand is present for an approach to detect and
locate tunnels, underground infrastructure, and for identifying
objects located within the ground. A threat is posed by tunneling.
Tunnels may be deeply bored. Deep urban bunkers with
interconnecting tunnels also may be present. These types of tunnels
are often used to smuggle illegal contraband into and out of a
country. Many of these facilities are deeply buried or
significantly hardened in an attempt to preclude detection and
characterization by sensors.
Various approaches that have been considered for detecting tunnels
include electromagnetic and gravity gradiometry, thermal, seismic,
or other nondestructive and noninvasive investigations. These
approaches have been used by active and passive systems through
unattended ground vehicles and unmanned aerial vehicles, as well as
other land mobile platforms as mountings for these types of
sensors. Invasive techniques that have been used include drilling
techniques for tunnel detection and verification. With respect to
detecting tunnels at different ranges, a need has developed for
detecting near surface tunnels. These types of tunnels typically
have a depth range anywhere between a few feet to a hundred feet or
more under the surface. Currently available techniques do not have
the depth range and resolution needed to detect tunnels at the
deeper end of this depth range.
SUMMARY
The advantageous embodiments of the present invention provide a
method and apparatus for detecting objects located underground. In
one advantageous embodiment, a detection system detects objects
having electrical non-linear characteristics located underground.
The detection system comprises a transmitter unit, a receiver, and
a processor. The transmitter transmits a plurality of pulsed radio
frequency signals having a first frequency and a second frequency
into a ground. The receiver monitors for a response radio frequency
signal having a frequency equal to a difference between the first
frequency and a second frequency, wherein the response radio
frequency signal is generated by an object having the non-linear
conductive characteristics in response to receiving the plurality
of electromagnetic signals. The processor is connected to the
transmitter unit and the receiver, wherein the processor controls
an operation of the transmitter unit and the receiver, wherein the
object is detected when the response radio frequency signal is
detected by the receiver.
In another advantageous embodiment, an apparatus comprises a
transmitter unit and a receiver. The transmitter transmits a
plurality of electromagnetic signals having a first frequency and a
second frequency into a ground. The receiver monitors for an
electromagnetic signal having a frequency equal to a difference
between the first frequency and a second frequency that is
generated by an object having an electrical non-linear conductive
characteristic in response to being exposed to the plurality of
electromagnetic signals. The object is detected when the
electromagnetic signal is detected by the receiver.
In a different advantageous embodiment, a method is used to detect
an object with electrical non-linear characteristics. A plurality
of electromagnetic signals having a first frequency and a second
frequency are transmitted into a ground. Monitoring is performed
for an electromagnetic signal having a frequency equal to a
difference between the first frequency and a second frequency,
wherein the electromagnetic signal is generated by an object in the
ground having an electrical non-linear characteristic in response
to receiving the plurality of electromagnetic signals. The object
having the electrical non-linear characteristic is detected when
the electromagnetic signal is detected.
The features, functions, and advantages can be achieved
independently in various embodiments of the present invention or
may be combined in yet other embodiments in which further details
can be seen with reference to the following description and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel features believed characteristic of the invention are set
forth in the appended claims. The invention itself, however, as
well as a preferred mode of use, further objectives and advantages
thereof, will best be understood by reference to the following
detailed description of an advantageous embodiment of the present
invention when read in conjunction with the accompanying drawings,
wherein:
FIG. 1 is a diagram illustrating a method and apparatus for
detecting structures buried under the ground in accordance with an
advantageous embodiment of the present invention;
FIG. 2 is a diagram of a detection system in accordance with an
advantageous embodiment of the present invention;
FIG. 3 is a diagram illustrating another configuration for a
detection system in accordance with an advantageous embodiment;
FIG. 4 is a diagram illustrating a detection system in accordance
with an advantageous embodiment of the present invention;
FIG. 5 is a diagram illustrating an example of data obtained using
a detection system in accordance with an advantageous embodiment of
the present invention;
FIG. 6 is a flowchart of the process for detecting an object with
electrical non-linear characteristics in accordance with an
advantageous embodiment of the present invention;
FIG. 7 is a flowchart of a process for transmitting electromagnetic
signals in accordance with an advantageous embodiment to the
present invention; and
FIG. 8 is a flowchart of a process for detecting a response signal
in accordance with an advantageous embodiment to the present
invention.
DETAILED DESCRIPTION
With reference now to the figures and in particular with reference
to FIG. 1, a diagram illustrating a method and apparatus for
detecting structures buried under the ground is depicted in
accordance with an advantageous embodiment of the present
invention. In these illustrative examples, non-linear ground
penetrating radar technology is used to detect objects, such as
tunnels and bunkers. In the depicted example, electromagnetic
pulses are launched into the ground and echoes from an underground
object are received and interpreted in an attempt to identify the
object. The different illustrative embodiments recognize that a
problem with this current method of using ground penetrating radar
is that finding an appropriate radio frequency to operate the
system is often difficult. The different embodiments recognize that
this difficulty lies in the contradictory capabilities and
limitations of low and high frequencies.
The different advantageous embodiments recognize that
electromagnetic techniques in which electromagnetic pulses are
launched into the ground have been used. Echoes from underground
objects or discontinuities are received and interpreted. This
technique is referred to as a ground penetrating radar and has been
used in the past to detect various underground discontinuities,
such as cables, pipes, cavities, and other objects intoned or
buried deeply in ice or other formations.
The different advantageous embodiments also recognize that one of
the challenges with the currently used ground penetrating radar
methods is to find an appropriate frequency of operation. Often
times, the frequencies either do not exist or are not available.
With respect to available frequencies, if a frequency of operation
is chosen to be too low, the available resolution is poor, making
results unusable. These types of frequencies are usually less than
10 MHz.
If the selected frequency is too high, the available pulse
penetration depth suffers. In other words, higher frequencies do
not penetrate into the ground as far. A high frequency is typically
considered a frequency greater than 1 GHz. As a result, high
frequency ground penetrating radars are typically only used in
applications in which objects are located in shallow depths, such
as inches rather than feet.
Thus, the different advantageous embodiments of the present
invention provide an improved ground penetrating radar technique.
This technique is based on electrical non-linear characteristics of
objects, such as surfaces of corroded conducting objects that are
located in the ground. The technique also may be based on corroded
objects located in underground tunnels. In these examples, a
corroded conductive object may be oxidized or rusted. The corrosion
causes a conductive non-linearity in a shallow layer on the surface
of a conducting object. The corroded or oxidized portion has a
different conductivity than the non-corroded portion. This
technique also may be applied to other electrical non-linear
characteristics of objects. For example, if an object contains two
different types of metals in layers, this non-linearity also may be
used to detect the object located under the ground. Another example
may be discarded electronic circuits with non-linear components,
such as diodes or transistors, embedded in them.
The different advantageous embodiments provide a system for
detecting underground objects, such as tunnel 100 and bunker 102
within ground 104. These and other types of objects may be detected
based on electrical non-linear characteristics of these objects.
This non-linearity is typically found in corroded conducting
elements within tunnel 100 and bunker 102. These elements also may
be located as objects within tunnel 100 or bunker 102.
Alternatively, these elements may be part of the infrastructure
making up tunnel 100, bunker 102 or electronic equipment.
In these illustrative examples, pulsed electromagnetic fields are
sent into ground 104. Aircraft 106 is an example of a source for
electromagnetic signals 108. Truck 110 is a source of
electromagnetic signals 112.
When electromagnetic signals 108 encounter an object that has
electrical non-linear characteristics, currents are induced during
the duration of these pulses. Any non-linearity within the object
results in some of these currents being converted to or rectified
into currents oscillating at the difference frequency between the
frequencies of the two pulsed signals.
These difference currents then reradiate as electromagnetic
radiation at the difference frequency. Some of these signals
propagate back towards the surface as response signals 114.
Response signals 114 may be detected by a receiver in aircraft 106
to identify the presence of a buried object, such as tunnel 100.
The receiver in aircraft 106 is set to detect signals at the
difference frequency. In a similar fashion, when truck 110
transmits electromagnetic signals 112, a portion of bunker 102
containing a non-linear conductive section generates response
signals 116 at the difference frequency. In these examples,
electromagnetic signals 112 are in the form of pulsed
electromagnetic radiation.
In yet another embodiment, portable instrument 118 may be employed
to generate electromagnetic signals 120, which cause currents to
occur in a non-linear conductive section within tunnel 100. As a
result, some of these currents generate response signals 122, which
are radiated back to portable instrument 118. In this type of
embodiment, portable instrument 118 may be moved and positioned by
person 124. With this type of implementation, portable instrument
118 is carried by person 124 and periodically placed on the ground
104.
The receivers in aircraft 106 and truck 110 are insensitive to the
outgoing signals in these examples. This insensitivity occurs, in
the depicted examples, because the receiver operates at a much
lower frequency, which is not related harmonically to either of the
two transmitted frequencies. As a result, the background noise is
essentially eliminated or greatly reduced. Further, higher power
transmitted pulses may be emitted without having to worry about
these pulses coupling into sensitive receiver circuits and blinding
the receiver.
Another benefit, in many of the embodiments, is that the response
generated by the buried objects in ground 104, such as tunnel 100
and bunker 102, travel only one way. Response signals 114, 116 and
122 travel toward the receiver. As a result, unwanted signals
occurring from echoes created by irrelevant strata or layers in the
soil, encountered by the outgoing signals, are eliminated. Also,
echoes created by shallow lying trash in the soil are
eliminated.
In these examples, two transmitting antennas are used in which each
antenna is tuned or selected to transmit a different frequency from
the other antenna. The different frequencies are generated by a
transmitter unit. The different frequencies are used to create a
difference frequency within the desired frequency range. This
difference frequency is in the range of frequencies detected by the
receiver in these examples. In these examples, the difference
frequency is equal to the difference between the first frequency
and the second frequency. The first frequency is at higher
frequency than the second frequency in these examples.
In one embodiment, pulsed electromagnetic signals of both
frequencies enter the ground and propagate until these signals
encounter a conductive object in which currents are induced. The
currents are induced during the duration of the electromagnetic
pulses. If the object contains a component with an electrical
non-linear characteristic, such as a corroded or rusted surface,
some of these induced currents are converted to currents that
oscillate at the difference frequency.
The currents then re-radiate electromagnetic signals at the
difference frequency. A portion of the signal propagates back
towards the surface and is captured as a response signal by the
receiving antenna. A receiver connected to the receiving antenna is
specifically tuned to the difference frequency. The received
difference frequency signals are then interpreted.
One advantage of using this type of ground penetrating radar system
is that the receiver is insensitive to outgoing transmitted
electromagnetic signals because the receiver operates at a much
lower frequency. This frequency is selected to be unrelated to the
frequencies of the transmitted signal.
Therefore, background noise is greatly diminished with this type of
system. Additionally, higher intensity transmitted pulses may be
emitted without having to worry about these high power outgoing
pulses coupling into sensitive receiver circuits and blinding the
receiver. Another benefit of the different advantageous embodiments
is that a received signal at the difference frequency travels only
one way. The path that the signal travels is from the object to the
surface. This type of propagation eliminates most unwanted signals
that may occur due to echoes created by irrelevant strata or layers
in the soil that may be encountered as the outgoing transmitter
pulses enter the soil.
Turning now to FIG. 2, a block diagram of a detection system is
depicted in accordance with an advantageous embodiment of the
present invention. In this example, detection system 200 is an
example of an apparatus that may be implemented for detecting
objects having electrical non-linear characteristics that are
buried under the ground. In particular, detection system 200 may be
implemented or located in a vehicle, such as, for example, aircraft
106 or truck 110 in FIG. 1. Also, detection system 200 may be
implemented as a portable instrument.
In this example, detection system 200 includes transmitter 202,
transmitter 204, and receiver 210. Detection system 200 also
includes antenna 211, antenna 212 and antenna 213. Processor 214,
memory 216 and display 218 also are located in detection system
200.
Transmitter 202 and transmitter 204 form a transmitter unit that
generates electromagnetic signals at different frequencies.
Antennas 211 and 212 receive electromagnetic energy from
transmitters 202 and 204, respectively, and radiate the
electromagnetic energy as electromagnetic signals 220 and 222.
Depending on the implementation, a single antenna may be used in
place of antennas 211 and 212. Transmitters 202 and 204 may be
designed to share a single antenna in this type of implementation.
In these examples, electromagnetic signals 220 and 222 take the
form of electromagnetic radiation emitted as pulses. Response
signals 224 collected by antenna 213 are routed to receiver 210.
Receiver 210 filters and amplifies response signals 224 for further
processing. This processing may include interpretation, storage,
and display data for response signals 224.
In these examples, transmitter 202 and transmitter 204 may generate
electromagnetic signals 220 and 222 having different frequencies.
For example, transmitter 202 may generate electromagnetic signals
220 that are emitted by antenna 211 with the first frequency f1.
Transmitter 204 may generate electromagnetic signals 222 that are
emitted by antenna 212 with a second frequency f2.
The frequencies at which transmitters 202 and 204 generate
electromagnetic signals 220 and 222 are controlled by processor 214
in these examples. Processor 214 acts as a controller to generate
pulses for electromagnetic signals 220 and 222 in these examples.
Processor 214 controls the timings of the leading edges of the
emitted pulses and the timing of the leading edge of the received
pulses. Information about the received pulse-widths may be used to
help determine the resonant nature (the Q) of electrically
non-linear objects.
In these embodiments, the pulse widths of the received signals in
response signals 224 will have to be referred to (compared to) the
pulse widths of the outgoing (transmitted) pulses. Processor 214
may perform these and other operations based on instructions stored
in memory 216. Response signals 224 received by receiver 210 may be
displayed on display 218. Further, display 218 may also provide
other information, such as the range or location of a response
identified by receiver 210. Display 214 is also used to display
cross-sections in depth of the soil as traversed on the surface
along a normally straight line.
In these advantageous embodiments, processor 214 identifies a
frequency at which a response is desired to be detected by receiver
210. Processor 214 sets receiver 210 to detect signals at this
identified frequency. Processor 214 sets transmitter 202 to
transmit electromagnetic signals 220 at a first frequency f1.
Transmitter 204 is set by processor 214 to transmit electromagnetic
signals 222 at a second frequency f2. In other embodiments, the
frequencies transmitted by transmitters 202 and 204 are fixed and
not changed or controlled by processor 214.
The difference between the first frequency f1 and second frequency
f2 is equal to a difference frequency that is set for receiver 210
in these examples. The frequency selected for transmitters 202 and
204 are such that they do not affect the electronics in receiver
210. Receiver 210 is not configured or programmed to detect signals
at the frequencies set for transmitters 202 and 204.
As an example, transmitter 202 may be set to transmit at 94 MHz
while transmitter 204 is set to transmit at 106 MHz The difference
between these two frequencies is 12 MHz Receiver 210 is set to
detect signals at the 12 MHz frequency.
With these frequencies, the typical penetration depth into the
ground at output power levels currently used with conventional
ground penetrating radar systems is approximately 60 to 100 feet.
In these examples, object 226 is located under ground 228. Object
226 contains electrical non-linear characteristics. All or a
portion of object 226 may contain these characteristics in these
examples.
When electromagnetic signals 220 and 222 reach object 226, currents
are induced within all conductive parts of object 226. Some of
these induced currents will convert to currents with difference
frequency, .DELTA.f in portions of the conductive parts of object
226 with non-linear characteristics. These currents, with frequency
.DELTA.f, result in the generation of an electromagnetic signal in
the form of response signals 224. Response signals 224 are captured
by antenna 210 in these examples.
Receiver 210 detects response signal 224 and sends this data to
processor 214 for processing and analysis. In these examples,
receiver 210 does not detect electromagnetic signals 220 and 222
because receiver 210 is set only to detect a frequency that is the
difference between the frequency transmitted by transmitter 202 and
the frequency transmitted by transmitter 204.
The electrical non-linear characteristics may be found in objects,
such as, for example, oil, gas, and water pipelines. Other examples
of objects that may have non-linear elements that are buried
include fuel tanks, water tanks, and cables. Electrical
non-linearities may be present in these objects due to corrosion in
a metallic portion of the object. The electrical non-linear
characteristic within the object causes a response signal that has
a frequency equal to the difference between the two transmitted
signals to be returned. This response is detected by receiver 210
in this example.
In these examples, the penetration of electromagnetic signals 220
and 222 increases as the frequencies used decrease. Resolution,
however, decreases as well, as the frequencies decrease. More
specifically, the spatial resolution decreases. In this
illustrative example, transmitter 202 and transmitter 204 may
continuously transmit at frequencies f1 and f2. With this type of
operation, receiver 210 detects only the frequency that is the
difference between those two frequencies.
As a result, response signals 224, when detected by receiver 210,
is processed by processor 214 indicating the presence of object 226
under ground 228. Further, with the movement of detection system
200 in a horizontal direction relative to the surface of ground
228, the shape of object 226 may be identified through continued
detection of response signals 224. The change in time at which
response signals 224 is received as detection system 200 moves may
be used to determine the shape and depth of object 226. This
information may be stored by processor 214 and memory 216 as
readings together with location (position) readings are taken by
detection system 200. The data stored in memory 216 may be
processed by processor 214 to generate an image of object 226 under
ground 228 and present it on display 218. This image may be a
vertical cross section.
Alternatively, processor 214 may set receiver 210 to detect signals
within a range of difference frequencies. In this manner, if
additional objects in addition to object 226 are located under
ground 228 with different electrical non-linear characteristics at
various different depths, these objects also may be detected by
detection unit system 200.
With reference now to FIG. 3, a diagram illustrating another
configuration for a detection system is depicted in accordance with
an advantageous embodiment. Detection system 300 includes
transmitter antennas 302 and 304 along with receiver antenna 306.
In these examples, transmitter antenna 302 transmits at frequency
f1, while transmitter antenna 304 transmits at frequency f2.
Receiver antenna 306 is designed to receive frequencies at
frequency .DELTA.f, which is a frequency having a difference
between frequency f1 and frequency f2 for transmitter antennas 302
and 304 in these examples.
In FIG. 3, antennas 302, 304 and 306 are placed on surface 308 of
ground 310. Antennas 302 and 304 may transmit electromagnetic
signals 312 and 314, at frequencies f1 and f2, respectively.
In this example, object 316 is located under ground 310. Non-linear
characteristics in object 316 result in response signals 318, which
are detected by receiver antenna 306. Response signals 318 are
emitted at the difference frequency .DELTA.f.
In these illustrative examples, many ground penetrating radar
applications require radio frequency pulses that are at low
frequencies and cannot be collimated. This type of situation may
occur with many soil types which absorb radiation at an increasing
rate starting at frequencies several hundred MHz and higher. With
other soil types, such as dry sand and ice, millimeter waves may be
used without much absorption. A collimated system, such as that
depicted in FIG. 4 shown below, may be implemented.
Detection system 300, in these examples, is especially useful with
wet soils in which low transmitter frequencies are required. For
this type of configuration for detection system 300, transmitter
antennas 302 and 304 may emit signals at or around 200 MHz plus and
minus 15 MHz. In these examples, transmitter antennas 302 and 304
are, for example, about one half meter long at each of these
frequencies. Receiver antenna 306 may be three to four meters long
and operate to receive response signals 318 at around 25-30 MHz in
this particular example. Of course, depending on the particular
implementation, there is a range of frequencies to choose from.
Turning next to FIG. 4, a diagram illustrating a detection system
is depicted in accordance with an advantageous embodiment of the
present invention. Detection system 400 is an example of another
configuration that may be used in a vehicle, such as aircraft 106
or in truck 110 in FIG. 1.
In this particular example, detection system 400 includes
collimated millimeter wave source 402, collimated millimeter wave
source 404, and receiver 406. Detection system 400 also includes
processor 408, storage device 410, and display 411. This type of
implementation may be used in situations when high frequencies,
such as frequencies in the 100 GHz range, can be used.
Processor 408 operates to control collimated millimeter wave source
402 and collimated millimeter wave source 404. Further, processor
408 receives data for signals detected by receiver 406. Processor
408 executes instructions that may be located in storage device
410. Results of response signals detected by receiver 406 may be
presented on display 411
In this example, detection system 400 generates electromagnetic
signals in the form of a single beam, beam 412. Beam 412 is
generated through a combination of beams 414 and 416 which are
generated by collimated millimeter wave source 402 and collimated
millimeter wave source 404, respectively. Collimated millimeter
wave source 404 generates beam 416 with a first frequency f1.
Collimated millimeter wave source 402 generates beam 414 with a
second frequency f2. These two beams are combined into beam 412
using polarization beam combiner 418.
Beam 412 is in essence a combined circularly polarized beam with an
interference difference frequency. This interference difference
frequency is the difference between frequency f1 generated by
collimated millimeter wave source 404 and frequency f2 generated by
collimated millimeter wave source 402. Beam 412 may be directed
into the ground in which object 420 is buried. Object 420 includes
electrical non-linear characteristics that causes currents at the
difference frequency to be induced in object 420.
Electromagnetic signals may be emitted from these currents in the
form of response signal 422. Object 420 generates response signal
422 with a frequency that is the difference between frequency f1,
generated by collimated millimeter wave source 404 and frequency
f2, generated by collimated millimeter wave source 402. This
frequency is also referred to as a difference frequency.
Response signal 422 is detected by receiver 406 which sends the
information in return signal 422 to processor 408 for processing.
Processor 408 may store information received in return signal 422
in storage device 410. Additionally, processor 408 may display this
information in display 411 in detection system 400.
In detection system 400, beam 412 is a directed beam that may be
used to search an area in the ground that has a radius or diameter
for beam 412. As a result, when a signal, such as response signal
422 is received by receiver 406, a user of detection system 400 is
able to identify object 420.
The collimated millimeter wave sources used in the radio frequency
identification units in FIG. 4 may be implemented using any
available collimated millimeter wave source. More information on
these types of wave sources and their configurations may be found
in U.S. Pat. No. 6,864,825 B2 and U.S. Pat. No. 7,142,147 B2.
Turning now to FIG. 5, a diagram illustrating an example of data
that may be obtained using a detection system, such as detection
system 200 in FIG. 2 is depicted in accordance with an advantageous
embodiment of the present invention. In this illustrative example,
a detection system, such as detection system 200 in FIG. 2 is
configured to transmit electromagnetic signals at 185 MHz and 215
MHz. The response signal received is at 30 MHz. Display 500 is
generated using the response signals received. Such an image, as an
example in display 500, would be generated as detection system 200
moved across the ground. Display 500 is an illustrative example of
a characteristic image (a vertical cross-section in the ground)
that can be generated using the different processes in the
advantageous embodiments.
Within display 500, gas pipe 502 and gas pipe 504 are present. Gas
pipe 502 and gas pipe 504 are illustrated in display 500 as a
result of signals at .DELTA.f is received from corroded metal gas
pipes in the ground. Further, the depth of these pipes below the
ground also can be identified based on the time it took for the
electromagnetic pulses to travel round-trip to the object and back
to the receiver antenna. In addition, display 500 also contains
shallower objects, such as sewer pipes 506 and 508 in these
examples. Other examples of objects that can be detected are an
electronic instrument control system, a computer, or communications
equipment located below or under the ground. These objects may be
located in a tunnel or a bunker in these examples.
With reference now to FIG. 6, a flowchart of a process for
detecting an object with electrical non-linear characteristics is
depicted in accordance with an advantageous embodiment of the
present invention. The process illustrated in FIG. 6 may be
implemented in a detection system, such as detection system 200 in
FIG. 2 or detection system 400 in FIG. 4.
The process begins by transmitting electromagnetic signals into the
ground in which these signals have a first frequency f1 and a
second frequency f2 (operation 600). In these examples, the
electromagnetic signals are a continuous stream of electromagnetic
pulses originating from two transmitters with carrier frequencies
f1 and f2. Thereafter, the process monitors for an electromagnetic
response signal having a difference frequency equal to a difference
between the first frequency and the second frequency (operation
602). A determination is made as the whether a response signal
having the difference frequency is detected (operation 604).
If a response signal with the difference frequency is detected, the
signal is processed to identify a set of objects (operation 606).
The set of objects may be one or more objects depending on the
number of objects in the ground having electrical non-linear
characteristics that generate a response signal at a difference
frequency. The process terminated thereafter.
With reference again to operation 604, if the response signal is
not detected, the process returns to operation 600 as described
above.
Turning now to FIG. 7, a process for transmitting electromagnetic
signals is depicted in accordance with an advantageous embodiment
to the present invention. The process illustrated in FIG. 7 may be
implemented in a system, such as detection system 200 in FIG. 2. In
particular, the different instructions here may be implemented in a
processor, such as processor 214 in FIG. 2.
The process begins by selecting a first frequency f1 and a second
frequency f2 (operation 700). These two frequencies are selected in
a manner to elicit a response from an object buried in the ground
in which an electrical non-linearity is present in the object. The
selection of the frequencies for the transmitters vary depending on
the application or the implementation.
Typically, in these examples, frequencies between 1 MHz and 1000
MHz are selected. In these particular examples, the transmit
frequencies for the first and second frequencies are 94 MHz and 106
MHz. The difference frequency is 12 MHz. This difference frequency
is the frequency at which a response signal is expected if a
metallic object with a non-linear feature is present.
As a result, the frequency selected may vary depending on the
penetration depth desired for the transmission and response to the
transmission of these electromagnetic signals.
Afterwards, the first and second frequencies are set for the
transmitters (operation 702). Electromagnetic signals are then
transmitted into the ground (operation 704) with the process
terminating thereafter. The transmission of these electromagnetic
signals may take various forms. For example, they may be in the
form of pulses that are repeated. Alternatively, the signals may be
transmitted as continuous wave radio frequency signals. The
transmission of these signals in operation 704 continue until the
process terminates in these examples.
The process illustrated in FIG. 7 may be repeated as often as
needed. Further, each time the process is repeated, the first
frequency and the second frequency may be changed such that the
difference frequency, which is a frequency equal to the difference
between the first frequency f1 and the second frequency f2, also
changes. This changing of the difference frequency may be used each
time the process is repeated to attempt to identify objects under
the ground that may have different electrical non-linear
characteristics that respond at different frequencies. The process
in FIG. 7 may be repeated such that a range of difference
frequencies may be detected. If the detection system has fixed
frequencies for the transmitters, steps 700 and 702 are omitted and
the process only involves transmitting the electromagnetic signals
into the ground.
Turning now to FIG. 8, a flowchart of a process for detecting a
response signal is depicted in accordance with an advantageous
embodiment to the present invention. The process illustrated in
FIG. 8 may be implemented in a detection system, such as detection
system 200 in FIG. 2.
The process monitors for a response on a difference frequency equal
to a difference between the first frequency and the second
frequency (operation 800). This monitoring is performed using a
receiver, such as receiver 210 in FIG. 2. A determination is made
as to whether a response signal with the difference frequency is
detected (operation 802).
If a response signal is not detected, the process returns to
operation 800 to continue to monitor for a difference frequency. As
the process loops between operations 800 and 802, the
electromagnetic signals continue to be pulsed or emitted as a beam
from the detection system.
Alternatively, the vehicle may be stationery or the detection unit
may be placed on the ground or a platform for use. If the
frequencies set for the transmitter cycle such that the difference
frequency changes, operation 800 monitors for the different
difference frequencies. In this manner, a range of difference
frequencies may be monitored to detect objects that may have
different electrical non-linear characteristics.
When a response signal having the difference frequency is detected
in operation 802, the data from the response signals is processed
(operation 804). This processing may include, for example,
identifying the location or depth at which the object is located in
the ground. Additionally, the data in the response signals may be
processed to generate an image of the object.
Next, the processed data is displayed (operation 806) with the
process terminating thereafter. This process may be repeated to
obtain images of an object in addition to merely locating an
object. An example of an image is depicted in display 600 in FIG.
6. In the depicted examples, this process may be performed while
the detection unit is moving in a vehicle, such as aircraft 106 or
truck 110 in FIG. 1.
The flowcharts and block diagrams in the different depicted
embodiments illustrate the architecture, functionality, and
operation of some possible implementations of apparatus, methods,
and computer program products. In this regard, each block in the
flowchart or block diagrams may represent a module, segment, or
portion of code, which comprises one or more executable
instructions for implementing the specified function or functions.
In some alternative implementations, the function or functions
noted in the block may occur out of the order noted in the figures.
For example, in some cases, two blocks shown in succession may be
executed substantially concurrently, or the blocks may sometimes be
executed in the reverse order, depending upon the functionality
involved.
Thus, the different advantageous embodiments of the present
invention provide a method and apparatus for detecting objects
located underground. In one advantageous embodiment, a detection
system detects objects having electrical non-linear characteristics
located underground. The detection system comprises a transmitter
unit, a receiver, and a processor. The transmitter transmits a
plurality of pulsed radio frequency signal having a first frequency
and a second frequency into a ground.
The receiver monitors for a response signal having a frequency
equal to a difference between the first frequency and a second
frequency, wherein the response radio frequency signal is generated
by an object having non-linear conductive characteristics in
response to receiving the plurality of electromagnetic signals. The
processor is connected to the transmitter unit and the receiver,
wherein the processor controls a selection of the first frequency
and the second frequency, wherein the object is detected when the
response signal is detected by the receiver. By sweeping through
the frequency ranges, additional information about an object buried
in the ground may be obtained.
The description of the present invention has been presented for
purposes of illustration and description, and is not intended to be
exhaustive or limited to the invention in the form disclosed. Many
modifications and variations will be apparent to those of ordinary
skill in the art. Further, different advantageous embodiments may
provide different advantages as compared to other advantageous
embodiments. The embodiment or embodiments selected are chosen and
described in order to best explain the principles of the invention,
the practical application, and to enable others of ordinary skill
in the art to understand the invention for various embodiments with
various modifications as are suited to the particular use
contemplated.
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